File - Ms Brown's Chemistry Page
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Measurements Using clear standards of measurements, we can communicate more effectively in answering simple questions. 1 1.1 What Chemistry Is About Measurements Mass How heavy is an egg? Volume How much space does an egg occupy? Density Does an egg size piece of steel or wood have the same mass? Pressure How hard is it to crush an egg by squeezing evenly from all sides? 2 1.1 What Chemistry Is About Measurements Mass How heavy is an egg? Volume How much space does an egg occupy? Density Does an egg size piece of steel or wood have the same mass? Pressure How hard is it to crush an egg by squeezing evenly from all sides? 3 1.1 What Chemistry Is About Mass The size (or volume) does not tell us how much matter there is. 4 1.1 What Chemistry Is About Mass Which of these has more mass? What are the standards of comparison? Mass of a 1-L bottle of water 5 Mass of a single peanut 1.1 What Chemistry Is About Mass The gram is a unit of mass Mass of a 1-L bottle of water 1,000 grams 6 Mass of a single peanut 1 gram 1.1 What Chemistry Is About Mass Remember: Size (volume) does not tell us how much matter there is. 1,000 g = 1 kg 7 1.1 What Chemistry Is About Measurements Mass How heavy is an egg? Volume How much space does an egg occupy? Density Does an egg size piece of steel or wood have the same mass? Pressure How hard is it to crush an egg by squeezing evenly from all sides? 8 1.1 What Chemistry Is About Volume Volume indicates an amount of space. The milliliter (mL) is a unit of volume. 9 1.1 What Chemistry Is About Volume You can measure the volume of a liquid using a graduated cylinder. 75 mL 10 1.1 What Chemistry Is About Volume You can measure the volume of a liquid using a graduated cylinder. 1 mL = 1 cm3 11 1.1 What Chemistry Is About Measurements Mass How heavy is an egg? Volume How much space does an egg occupy? Density Does an egg size piece of steel or wood have the same mass? Pressure How hard is it to crush an egg by squeezing evenly from all sides? 12 1.1 What Chemistry Is About Measurements Mass How heavy is an egg? Volume How much space does an egg occupy? Density Does an egg size piece of steel or wood have the same mass? Pressure How hard is it to crush an egg by squeezing evenly from all sides? 13 1.1 What Chemistry Is About Accuracy and precision Is the mass exactly 10.0 g? Could it be 9.96 g? 10.04 g? We don’t know since any mass between 9.95 g and 10.05 g would round off to 10.0 g 14 1.1 What Chemistry Is About Accuracy and precision Measurements that are not accurate could lead you to the wrong conclusion. If a measurement is not precise, you may not be able to tell the difference between agreement and disagreement. 15 1.1 What Chemistry Is About Significant figures Do you record 10 g or 10.0 g? Does it make a difference? 16 1.1 What Chemistry Is About Significant figures Do you record 10 g or 10.0 g? Does it make a difference? Yes, it makes a difference in precision 17 1.1 What Chemistry Is About If you record “10 g” 9 10 11 If you record “10.0 g” 18 1.1 What Chemistry Is About Precision and accuracy What value should be recorded for the volume measurement in the picture? 19 1.1 What Chemistry Is About Precision and accuracy What value should be recorded for the volume measurement in the picture? 20 Asked: The value with the correct number of significant figures Given: You can estimate to a tenth of the graduation of a cylinder or ruler Relationships: The last digit on the right is assumed to be plus or minus one-tenth. 1.1 What Chemistry Is About Precision and accuracy What value should be recorded for the volume measurement in the picture? 21 Asked: The value with the correct number of significant figures Given: You can estimate to a tenth of the graduation of a cylinder or ruler Relationships: The last digit on the right is assumed to be plus or minus one-tenth. Solve: The meniscus is right on 18, so estimate 18.0 mL. Answer: 18.0 mL Discussion: The real value is confidently known to be between 17.9 and 18.1 mL. 1.1 What Chemistry Is About Science encompasses very large and very small objects. Large Small The scientific notation is a shorthand system to write very large and very small numbers 22 1.1 What Chemistry Is About Scientific notation mantissa 1,500 = 15 x 100 power of 10 23 1.1 What Chemistry Is About Scientific notation mantissa 1,500 = 15 x 100 = 102 100 = 10 x 10 = 102 24 exponent 1.1 What Chemistry Is About Scientific notation mantissa 1,500 = 15 x 100 = 102 mantissa 1,500 = 1.5 x 1,000 = 103 25 1.1 What Chemistry Is About Scientific notation 1,500 in scientific notation: 1.5 x 103 mantissa 1,500 = 1.5 x 1,000 = 103 26 1.1 What Chemistry Is About Scientific notation 40,000,000 = 4 x 107 3,600 = 3.6 x 103 83,100 = 8.31 x 104 27 1.1 What Chemistry Is About Scientific notation mantissa 0.0015 = 1.5 x 0.001 power of 10 28 1.1 What Chemistry Is About Scientific notation mantissa 0.0015 = 1.5 x 0.001 = 10–3 A negative exponent means: the number is smaller than 1 does not mean: the whole number is negative 29 1.1 What Chemistry Is About Scientific notation mantissa 0.0015 = 1.5 x 0.001 = 10–3 0.0015 in scientific notation: 1.5 x 10–3 30 1.1 What Chemistry Is About Scientific notation 0.000 000 4 = 4 x 10–7 0.003 6 = 3.6 x 10–3 0.000 083 1 = 8.31 x 10–5 31 1.1 What Chemistry Is About Scientific notation Convert 0.00065 to scientific notation. 32 Asked: The number in scientific notation Given: 0.00065 as a decimal number Relationships: 0.0001 104 1.1 What Chemistry Is About Scientific notation Convert 0.00065 to scientific notation. 33 Asked: The number in scientific notation Given: 0.00065 as a decimal number Relationships: 0.0001 104 Answer: 6.5 104 1.1 What Chemistry Is About Scientific notation Using scientific notation on a calculator 34 1.1 What Chemistry Is About Unit conversions Convert $1.25 / L to dollar per gallon. 35 1.1 What Chemistry Is About Unit conversions Convert $1.25 / L to dollar per gallon. 36 Asked: A value in dollars per gallon Given: $1.25/L Relationships: 1 gallon = 3.785 L 1.1 What Chemistry Is About Unit conversions Convert $1.25 / L to dollar per gallon. 37 Asked: A value in dollars per gallon Given: $1.25/L Relationships: 1 gallon = 3.785 L Solve: $1.25 3.78 L $4.73 L 1 gallon gallon Answer: $4.73/gallon 1.1 What Chemistry Is About Measuring physical properties Mass Volume Density Pressure Precision vs. accuracy grams liters grams per liter atmospheres, psi Scientific notation 38 40,000,000 0.000 000 4 = 4 x 107 = 4 x 10–7 1.1 What Chemistry Is About
